Soft crepe paper machine and press section thereof The present invention relates to a machine for manufacturing a web of soft crepe paper, comprising -a wet section, having a former and a press section, which press section comprises -a press including a first press element and a second press element, which press elements define a press nip between them, -a press felt carrying the web and running through said press nip, and -a suction device arranged in the loop of the press felt before said press nip and at a distance from said second press element and having a curved suction zone, the press felt running over said suction zone and the suction device and the press felt being arranged so that the press felt has a large wrap angle around the suction device, and -a drying section including at least a first drying cylinder, which forms said second press element.

The invention also relates to a press section in a machine for manufacturing a web of soft crepe paper, comprising -a press including a first press element and a second press element, which press elements define a press nip between them, the second press element being formed by a drying cylinder in the drying section of the machine, -a press felt carrying the web and running through'said press nip, and -a suction device arranged in the loop of the press felt before said press nip and at a distance from said second press element and having a curved suction zone, the press felt running over said suction zone and the suction device and the press felt being arranged so that the press felt has a large wrap angle around the suction device.

US 5,230,776 and US 3,691,010 describe conventional machines with two presses, in both of which the drying cylinder acts as a counter roll and the first press has a suction press roll that can be crowned. To avoid running problems, the press felt must be conveyed out in a side loop between the two press nips. The web reaches the first press nip with a dry-solids content of about 10-15 per cent. In a modified second embodiment of the machine in accordance with US 5,230,776, the second press roll is disconnected and the web-carrying forming wire is extended to the first suction press roll while an open belt of wire type is substituted for the press felt to enclose the web between it and the forming wire, creating a sandwich construction that can be provided with airflow-generating means. Suction boxes can be arranged upstream of the sandwich construction in the loop of the forming wire. The known machine can thereby be modified, from one operational embodiment to another that provides a higher dry-solids content, and be adapted to different market needs. Thus, in the second embodiment, which is of a relatively complicated construction, the suction press roll is used in combination with an open belt and not solely with a press felt, and the suction means, located upstream of the suction press roll, are not arranged in a press-felt loop running through the press nip.

US 4,055,461 describes a soft crepe paper machine having a pick-up suction roll and a press section with double press nips against a suction press roll, where the web is compressed in the first press nip before reaching the second press nip against the drying cylinder, which affects the bulk detrimentally.

So-called through-air drying is used to increase the dry-solids content of the web before the drying cylinder.

The increased dry-solids content allows the nip pressure to be reduced substantially in the subsequent press nip,

in comparison with a conventional soft crepe paper machine, so that a desired high bulk is obtained.

However, a through-air dryer represents high capital expenditure and requires additional space in the machine line. Furthermore, it has high running costs, as hot air is utilized.

In accordance with another technique for obtaining an increased dry-solids content before the press nip, a suction device is utilized and the pressing takes then place in an extended shoe press nip. A machine constructed in accordance with this technique is described in EP 0 926 296. The press is a shoe press formed by a shoe press roll and the drying cylinder as counter roll. The suction device is shown in the patent specification as a suction roll arranged before the extended shoe press nip at a distance from the drying cylinder. The suction roll enables the dry-solids content of the web to be increased to a high level before the press nip. Such an increased dry-solids content before the press nip is thus advantageous, as it becomes possible thereby to reduce the compression pressure in the press nip so that a substantially increased bulk can be obtained since the web is compressed to a lesser extent. However, a shoe press roll is a relatively complicated construction, entailing high capital expenditure and requiring special operational control.

Machines with similar shoe presses are described in EP 0 851 059 and EP 0 854 229, although, in both cases, a suction roll in the specified position before the shoe press nip is lacking.

It is therefore an object of the present invention to provide a soft crepe paper machine having a simpler press section, which results in reduced capital expenditure and enables a paper web with high bulk to be manufactured in

a simpler and more cost effective way than has heretofore been possible, as well as enabling the user of the soft crepe paper machine to choose press elements in accordance with his specific needs.

The machine and press section in accordance with the invention are characterized in that said first press element comprises (a) a solid press roll, (b) a suction press roll, (c) a variable crown press roll, (d) a variable crown press roll, the crown curve of which is controllable within at least two zones of the press roll, or (e) a press roll having at least two of the properties of the press rolls (a) to (d).

The invention is further described in the following with reference to the drawings.

Figure 1 shows schematically a soft crepe paper machine with a press section in accordance with a first embodiment.

Figure 2 shows schematically a soft crepe paper machine with a press section in accordance with a second embodiment.

Figure 3 shows schematically a soft crepe paper machine with a press section in accordance with a third embodiment.

Figure 3a is a longitudinal sectional view of one of the end portions of a variable crown press roll in the press section in accordance with Figure 3.

Figure 4 shows schematically a soft crepe paper machine with a press section in accordance with a fourth embodiment.

Figure 4a is a longitudinal sectional view of a zone-controllable, variable crown press roll in the press section in accordance with Figure 4.

Figures 1-4 show schematically parts of paper machines for manufacturing soft crepe paper such as tissue and other creped hygiene paper products. Each paper machine comprises a wet section 1 and a drying section 2. The wet section 1 comprises a former and a press section. The former has a headbox 4, an inner, carrying forming clothing 5, an outer, covering forming clothing 6, a forming roll 7 and a breast roll 8. The forming roll 7 and the breast roll 8 are arranged in proximity to each other so that the two forming clothings 5,6 run together on the forming roll 7 whilst defining a wedge-shaped gap between them before they run together, the headbox 4 delivering a single-or multi-layer jet of stock into said gap to form a paper web 9 by way of the stock being dewatered. The two forming clothings 5,6 run together over the forming roll 7 and then in individual loops over a plurality of rolls 10 arranged to move, guide, align and stretch the forming clothings 5,6.

The press section comprises a roll press 11, consisting of a first press roll 12 and a second press roll 13, which press rolls 12,13 define a press nip between them.

It is preferable for the press section to have only one press, i. e. roll press, as shown in the drawings, so that no additional press nip is formed against the second press roll 13 or against the first press roll 12 or defined by any two other press elements. Further, the press section has a press felt 14, running through the press nip and in a loop around a plurality of rolls 15,

arranged to move, guide, align and stretch the press felt 14. Devices (not shown) for cleaning the press felt 14 are located after the press nip. In the loop of the press felt 14, there is a suction device 16, which, in the embodiment shown, consists of a suction roll that is arranged just before the press nip and from which the press felt 14 carries the web 9 so that the side of the web 9 facing away from the felt is free from contact with any structural element before the press nip. The suction device 16, which has a curved suction zone 3, is so arranged in relation to the nearest upstream guide roll 15 and the downstream press roll 12 that the press felt 14 has a high wrap around the suction device 16, i. e. the press felt 14 and the paper web 9 carried by the same change direction at a large angle over the suction zone 3. The wrap angle should be at least 100°, preferably at least 110°. In experiments performed with a suction roll, the wrap angle has been about 140°. The suction zone 3 encloses a sector angle corresponding to said wrap angle and extends within the same. The large wrap angle contributes to increased dewatering. The suction device 16 is arranged to provide the paper web 9 with a dry-solids content of at least 15 per cent, preferably at least 20 per cent and most preferably at least 25 per cent.

The drying section 2 comprises a crowned drying cylinder 17 having a relatively large diameter and a polished envelope surface. The drying cylinder 17, which preferably consists of a Yankee cylinder, is covered by a hood 18, in which hot air is blown at high speed against the paper web 9. The paper web is creped away from the drying cylinder 17 with the aid of a crepe doctor 19 to obtain desired creping, whereupon the finished creped paper web 9'is reeled onto a reel (not shown). The drying cylinder 17 also forms said second press roll 13 in the roll press 11 of the drying section 2. Said suction roll

16 is arranged at a distance from the drying cylinder 17 so that no press nip is formed between them and so that the web 9 does not come into contact with the envelope surface of the drying cylinder 17 until it reaches the press nip or immediately before.

In the paper machines in accordance with Figures 1 and 2, the inner carrying forming clothing 5 consists of a forming felt, the loop of which is extended to the press section 2 so that it also acts as said press felt 14.

In the paper machines in accordance with Figures 3 and 4, the inner carrying forming clothing 5 consists of a forming wire, the loop of which encounters the loop of the press felt 14 in a transfer zone 20 for transferring the web 9 to the press felt 14, a suction shoe 21 being arranged within said transfer zone 20 in the loop of the press felt 14.

In the paper machine in accordance with Figure 1, the first press roll 12 of the roll press 11 consists of a press roll 12a with a solid shell 22 that can be smooth, grooved or blind-drilled. The press roll 12a can be straight depending on the crown of the drying cylinder 13, amongst other things, but is preferably crowned so that it has a crown curve corresponding to a certain compression pressure to obtain profiles for compression-pressure and dry-solids content that are as uniform as possible after pressing without zones with higher moisture occurring in the web after the press nip.

In the paper machine in accordance with Figure 2, the first press roll 12 of the roll press 11 consists of a suction press roll 12b that can be straight depending on the crown of the drying cylinder, amongst other things, but which is preferably crowned so that it has a crown curve corresponding to a certain compression pressure to

obtain profiles for compression-pressure and dry-solids content that are as uniform as possible without zones with higher moisture occurring in the web after the press nip. A special advantage of the suction press roll 12b is that it also has a cleaning effect on the press felt 14 so that special cleaning means arranged after the press nip can be completely or partly reduced and the frequency of felt replacements can be diminished.

In the paper machine in accordance with Figure 3, the first press roll 12 of the roll press 11 consists of a variable crown press roll 12c, the shell of which can be smooth, grooved or blind-drilled. The crown curve of the press roll 12c can be changed during operation to be adapted to a pre-determined compression pressure so that as uniform as possible profiles for compression-pressure and dry-solids content are obtained without zones with higher moisture occurring in the web after the press nip.

If the machine is to manufacture a soft crepe paper of a different desired grade with respect to bulk and strength, the crown curve is changed to correspond to a new compression pressure so that as uniform as possible profiles for compression-pressure and dry-solids content for the new setting are obtained without zones with higher moisture occurring in the web after the press nip.

Figure 3a shows schematically a longitudinal section of one of the end portions of the variable crown press roll 12c, the shell 22 of which surrounds an upper pressure chamber 23, connected to a pressure source (not shown).

The pressure chamber 23 extends between the end walls 24 of the press roll, the ends of the shell 22 being rigidly attached to said end walls. Changing the pressure in the pressure chamber 23 produces a corresponding change of the crown curve within the press nip. The shell 22 also surrounds a lower pressure chamber 25 having a pre-determined lower pressure than the upper pressure

chamber 23. The pressure chambers are separated by opposite, axial sliding sealings 26.

In the paper machine in accordance with Figure 4, the first press roll 12 of the roll press 11 consists of a zone-controllable, variable crown press roll 12d, the shell 22 of which can be smooth, grooved or blind-drilled. The crown curve of the press roll 12d can be changed during operation to be adapted to a pre-determined compression pressure so that as uniform as possible profiles for compression-pressure and dry-solids content are obtained without zones with higher moisture occurring in the web after the press nip. If the machine is to manufacture a soft crepe paper of a different desired grade with respect to bulk and strength, the crown curve is changed to correspond to a new compression pressure so that as uniform as possible profiles for compression-pressure and dry-solids content for the new setting are obtained without zones with higher moisture occurring in the web after the press nip. In this embodiment, the crown curve can additionally be influenced zone by zone so as thereby to adjust the compression-pressure profile within the corresponding parts so that the same becomes even more uniform and straight than is possible with a variable crown press roll that is not zone-controllable to obtain a dry-solids content profile after the press nip that is correspondingly more uniform and straight. Figure 4a shows schematically a longitudinal section of the zone-controllable, variable crown press roll 12d, which has an axial row of pressing members 27 equidistantly arranged inside the shell 22 and opposite to the press nip. With respect to their pressing influence on the shell 22, the pressing members 27 are divided into two outer groups 28,29 and an inner or intermediate group 30 between them, the groups 28,29,30 of pressing members 27 being actuated independently of each other via

separate ducts 31,32 and 33, respectively, provided with valves. Each group of pressing members 27 actuates its corresponding axial zone of the shell and, consequently, the crown curve.

The drying cylinder 13 is crowned in at least the embodiments in accordance with Figures 1-3. A special advantage of the embodiment in accordance with Figure 4 is that the drying cylinder 13 does not need to be crowned.

In all cases, the press roll 12 is driven and its shell 22 comprises an outer layer of a rubber material or a rubber-like material. The thickness and softness of the rubber layer is chosen as needed. A certain compression of the rubber layer occurs in the press nip so that it is extended somewhat in the direction of movement of the web. It should thus be understood that the thickness and softness of said parameters determine the length of the extended press nip at a given compression pressure. The linear load, which corresponds to the impulse of pressure, is a function of compression pressure, pressing time and machine speed. If the compression pressure is increased, the pressing time will increase as well, since the rubber layer of the shell is compressed further so that the press nip becomes longer.

Each one of the described roll presses is of a substantially simpler construction than the known shoe press in accordance with EP 0 926 296, which results in reduced capital expenditure and enables the manufacture of a soft crepe paper with a bulk substantially as high as with the said known shoe press, but in a simpler and more cost effective way. Furthermore, the user has the advantageous opportunity of choosing, out of the alternatives, that press roll which is most suited to the specific needs of the user as regards whether the same

grade is to be produced for a longer period of time (suitably press roll 12a or 12b) or different grades are to be produced alternatingly in smaller series (suitably press roll 12c or 12d).

In a further embodiment (not shown) the first press element is a press roll having at least two of the properties of the four press rolls 12a to 12d described above, such as, for instance, a variable crown suction press roll.